1. Field of the Invention
The present invention relates to an optical element rotating device suitable for a liquid-crystal projector system with a liquid-crystal panel which device can rotate the optical element about its optic axis, and specifically to an electromagnetic solenoid which can reciprocatingly rotate an optical element at a predetermined cycle.
2. Description of the Prior Art
As is well known, a liquid-crystal projector system employs a liquid-crystal panel, a light source, a projection lens set consisting of a group of projection lenses and a movable focus-adjustment lens, and a control circuit arranged for adjusting the focus of the focus adjusting lens. In recent years, the video technologies teach an improved liquid-crystal projector which is capable of alternately displaying a video signal included in an odd field and a video signal included in an even field, at a predetermined period of time by way of the same pixels of the liquid-crystal panel, and vertically offsetting both projected positions of the picture images of the respective fields to each other by one pixel in synchronization with a vertical synchronizing signal in the video signal, so as to distinctly display the projected images. In the conventional liquid-crystal projectors, it is desired to provide a more precise and superior vertical offsetting technologies for both projected positions of picture images, respectively included in an odd field and an even field, on a screen.